Apparatus for controlling highway crossing signals



Dec. 10, 1940.

R. R. Y 'KEMMERER APPARATUS FOR CONTROLLING HIGHWAY CROSSING SIGNALS Filed Sept. .15, 19:58

3 Sheets-Sheet l S Ralphll. '5

IN NTOR BY M HIS ATTORNEY Dec. 10, 1940. 2,224,395.

APPARATUS 'FOR CONTROLLING HIGHWAY caussme SIGNALS R. R. KEMM ERER Fi ledsept. 15, 1938 :5 Sheets-Sheet 2 kv NANNY H WN IN NTOR Ralplzllli' HA5 ATTORNEY Dec. 10, 1940. R.,R. KEMMERER 2.2243

APPARATUS FOR CONTROLLING HIGHWAY CROSSING SIGNALS Filed Sept. 15, 1938' 3 Sheets-Sheet 3 1 1? ram ARI] A]? mvmon Hal M212. mepel. BY v [115 ATTORN EY Patented Dec. 10, 1940 UNITED STATES PATENT OFFICE APPARATUS FOR CONTROLLING HIGHWAY CROSSING SIGNALS Ralph R. Kemmerer, Swissvale, Pa., assignor to The Union Switch & Signal Company, Swissvale, Pa., a corporation of Pennsylvania Application September 15, 1938, Serial No. 230,082

12 Claims. (01. 246130) My invention relates to apparatus for control- Fig. 4 is a fragmentary diagrammatic view ling highway crossing signals, that is, to means showing a modified form of train detecting for controlling a signal of the type which is means embodying my invention,

placed at the intersection between a railway and Fig. 5 is a fragmentary diagrammatic view 5 a highway for the purpose of warning users of showing another modified form of train detecting 5 the highway when a train is approaching. means embodying my invention,

It is essential that signals of this type be oper- Fig. 6 is a fragmentary diagrammatic view ated long enough in advance of the arrival of showing a diiferent form of a train detecting the train at the intersection to enable users of means embodying my invention,

the highway to clear the intersection. It is de- Fig. 7 is an enlarged sectional view taken sub- 10 sirable also that the signal not be operated too stantially along the line VII-VII of Fig. 6, and long in advance of the arrival of a train at the Figs. 8 and 9 are fragmenta y diagrammatic intersection as this unduly delays users of the views showing still diiierent forms of train dehighway and tends to create disrespect for the tecting means provided by my invention.

.15 warning signal. Referring to Figs. 1A and 1B of the drawings,

It is customary to initiate operation of a sigthe reference character X designates a stretch of nal of this type when a train reaches a point railway track over which trafiic moves in both in the track a predetermined distance from the directions. The track stretch has rails I and intersection. This point is located far enough 2 which are divided y insulated Jo ts 3 nt 3.0 from the intersection so that on movement of a sections IT and 2T, while the track stretch infast train over the track, the warning signal cludes an intersection with a highway designated is operated for the proper time interval before by the reference character H. The insulated the train reaches the intersection. On movement joints 3 separating the track sections iT and 2T of a slow-train over the track, if operation of the are located adjacent the intersection.

5 crossing signal is initiated when the train reaches The highway crossing H is protected by a sigthe same predetermined point in the track, the nal S which may be of any suitable type, such as signal will be operated for an unduly long period a bell or light signal or a combination of both. of time before the train reaches the intersection. The signal S is controlled by a relay K which is It is an object of my invention to provide a of the type known as an interlocking relay and control system for a signal of the type described is provided with a pair of windings 5 and 5 which 30 and incorporating means governed in accordance are responsive to the supply of alternating curwith the speed of the train traveling on the track rent.

for determining the time at which operation of The details of the construction of the interthe crossing signal is initiated to lthereby mainlocking relay K are not a part of the present tain the period of operation of the signal subinvention and any suitable relay of this type may stantially uniform irrespective of speed of the be employed. The relay K has a movable contrain approaching the intersection. tact I controlled by the winding 5, and a movable A further object of my invention is to provide contact 8 controlled by the winding 6. The conimproved apparatus of the type described and tacts and Bare held in their open or picked 0 which does not necessitate the use of short track up positions as long as the windings 5 and 8 40 circuits. are energized, while on deenergization of either Another object of my invention is to provide of these windings the contact controlled by that improved apparatus for controlling a highway winding is released and moves to its closed posicrossing signal. tion in which it completes the circuit from one Other objects of my invention and features of terminal B of a suitable source of current to the 45 novelty will be apparent from the following demechanism of the signal S. The mechanism of scription taken in connection with the accomthe signal S is directly connected to the other terpanying drawings, in which minal C of that source of current.

Figs. 1A and 1B taken together are a diagram The interlocking relay K is constructed in such of a system embodying my invention. a manner that when one winding of the relay 50 Fig. 2 is an enlarged view showing a current is deenergized as a result of occupation of a track transformer employed in the system shown in section by a train, and the contact controlled by Figs. 1A and 1B, that winding drops to its closed position, the

Fig. 3 is a diagram of a modification of the movable contact controlled by the other winding 5 system shown in Figs. 1A and 1B, is held in its open position so that when the t 5 closed position.

associated becomes occupied and said other winding is deenergized, the contact controlled by-f.t1ie,f f

other winding is prevented from moving to The internal construction of the relay K is also such that if, while the second winding is deenergized, the first winding becomes energized as a result of movement of a train outof the track section with which the winding is associated, the movable contact controlled by that winding is caused to move from its closed to its open position, thereby interrupting the circuit to the mechanism of the signal S. When this contact picks up it continues to maintain the contact controlled by the other or second winding in its picked up or opentposition as long as the other winding is deenergized. When the other or second winding is again energized the control of the movable con- 20 tact associated with that winding by the movable v contact associated with the first winding is termin'ated, and on subsequent deenergization of the other winding at a time when the first winding is energized the movable contact associated with the other winding may move to its closed position.

The equipment associated with each of the track sections IT and 2T for controlling the supply of current to a winding of the relay K is substantially the same as the equipment associated with the other track section. Accordingly only the equipment associated with the track section IT at the left of the intersection His shown in the drawings. It will be understood, however, that similar equipment is associated with the 35 track section 2T at the right of the intersection H.

The track section IT has associated therewith an alternating current track relay ITR having a control winding 9 connected across the track rails I and 2 at a point adjacent the end of the track section IT remote from the intersection H, while the local winding I of the track relay ITR is connected by wires. I 2 and I4 to a suitable source of alternating current, such as a local commer- 45 cial source of power, the terminals of which are designated by the reference characters BX and CX. a

The track section IT has associated therewith a track transformer ITRA having its primary 50 winding I5 connected to the wires I2 and I4, and thereby to the terminals BX and UK of the same source of alternating current as the local windmg III of the track relay ITR. The secondary.

such as an impedance I1, with the track rails I and 2 at a point adjacent the end of the track section IT adjacent the intersection H.

The track section IT has associated therewith 60 means for measuring the speed of a train traveling in such section to thereby determine the point in such section to which a train approaching the intersection H must advance before the circuit for supplying current to the winding 5 of the in- 65 terlocking relay K is interrupted to thereby initiate operation of thecrossing signal S.

As shown in the drawings, one terminal of the winding 5 of the relay K is connected to a branch of the wire I 2, and thereby to the terminal 'CX of 7 the source of alternating current. The. other terminal of the winding 5 is connected by a wire 20 to a branch of the wire I4, and thereby to the terminal BX of the source of alternating current. The circuit through the wire 20 is controlled by train detecting apparatus associated with stations 2,224,395 track section with which said other winding is I A, B and C located at spaced points in the track section IT and responsive to movement of a train thrfoughthe track section.

Construction of 'train detecting means The apparatus associated with the station A includes train detecting means incorporating current transformers AI and A2 associated with the track rails I and.2. .The construction of the current transformer AI is shown in detail in Fig. 2 of the drawings. The current transformers employed at the various stations are all of similar construction and the construction of the transformer AI only will be described in detail.

, As shown in Fig. 2 of the drawings, the current transformer AIv comprises a generally U-shaped core member 22 which extends beneath the track rail I and has arms 23 and 24 extending upwardly adjacentthe sides of the track rail. Suitable'blocks 25 and 2B of non-magnetic material are positioned between the arms 23 and 24, while a bolt 21 also of non-magnetic material extends through the arms 23 and 24, the blocks 25 and 26, and the track rail I to secure the core member 22 to the track rail.

The' arm 23 of the core member 22 extends nearly to the top of the track rail I. The arm 24 is located on the side of the track rail I adjacent the track rail 2, while the arm 24 is held by the block 25 spaced from the side face of the head of the track rail a distance suificient to enable the flange on a vehicle wheel to pass between the arm 24 and the rail. The core member 22 has mounted thereon a winding 29. I

The windings 29 of the current transformers Aland A2 are connected in series with each other, and in series with a condenser CI with the primary winding 30 of a grid transformer ATS,

The station A has associated therewith atube AVI having a'grid 32, an anode 33, and a cathode 34 in the form of a heated filament. These elements are mounted in a sealed envelope which is filled to a low pressure with a suitable inert gas. The tube AVI is of the type known as a grid-glow tube and is characterized by the fact that the flow of current between the anode and the oathode of the tube is controlled by the relationship of the grid potential to the anode-cathode potential. in such a manner that the tube is substanproper potential in relation to the anode-cathode potential. When the grid is supplied with this potential the tube breaks down and becomes conducting.

One terminal of the secondary winding 35 of the grid transformer ATE is connected to the anode 33 of the tube AVI, while the other terminal of the Winding 35 is connected in series with a resistor or grid leak ARI with the grid 32 oi the tube AVI.

The filament or cathode 34 of the tube AVI is connected to the terminals of the secondary winding 38 of the plate and filament transformer ATI. The primary winding 40 of the transformer ATI is supplied with alternating current by branches of the wires I2 and I4. The grid 32 of the tube AVI is connected in series with a grid condenser AC2 with a mid tap of the secondary winding 38 of the transformer ATI, and thereby with the cathode or filament 34.

The train detecting means at station A includes a direct current relay AREI. One termiof the winding 42 is connected to the mid tap of the winding 38 of the transformer ATI and thereby to the tube cathode 34. The other terminal of the winding of the relay AREI is connected in series with a current limiting resistor AR2 with the anode 33 of the tube AVI. A by-Dass condenser AC3 is connected in multiple with the winding of the relay AREI.

In operation, alternating current supplied from the wires I2 and I4 energizes the primary winding 40 of the transformer ATI, thereby causing current to be induced in the secondary windings 38 and 42. Current induced in the winding 38 is supplied to the filament 34 of the tube AVI and heats this filament. Current induced in the winding 42 establishes a potential difference between the anode 33 and the cathode or filament 34 of the tube AVI.

The potential difference impressed between the anode and the cathode of the tube AVI is less than the critical or breakdown value under conditions of zero or low grid potential. Accordingly, in the absence of greater than normal potential supplied to the tube grid, no current flows between the anode and the cathode of the tube and hence the relay AREI remains deenergized.

Alternating current is also supplied from the wires 12 and I4 to the primary winding I5 of the track transformer ITRA, and from the secondary winding N5 of the transformer ITRA current is supplied to the track rails I and 2.

The current which is supplied to one of the track rails of track section VI flows through this rail to the other end of the track section, through the control winding 9 of the track relay TR to the other track rail, and thence through that track rail to the transformer ITRA.

On the flow of current through the track rails magnetic lines of force are caused to flow in the magnetic core members 22 of the current transformers Al and A2. As a result of the flow of these lines of force through the core members,-

current is induced in the windings 29 of these transformers.

The current which is induced in the windings 29 of the current transformers AI and A2 is supplied therefrom to the primary winding 30 of the grid transformer ATS. On the supply of current to the winding 30 current is induced in the secondary winding 36 and flows therefrom to a circuit which includes the grid leak ARI, the grid condenser AC2, the winding 42 of the transformer ATI, by-pass condenser AC2, and resistor AR2.

. The anode 33 of the tube AVI is connected'to this circuit at a point adjacent one terminal of the secondary winding 36. The grid 32 of the tube AVI is connected to this circuit at a point intermediate the grid leak and the grid condenser, while the tube cathode 34 is connected by means of the center tap on the transformer secondary winding 38 to this circuit at a point on the side of the grid condenser AC2 remote from the point of connection of the grid 32 with the circuit.

As a result of this circuit arrangement when current is supplied to this circuit from the secondary winding of the transformer ATS, the potential on the grid is maintained at a value above that on the cathode, and the various circuits are arranged so that the potential difference between the grid and the cathode is in the same phase relationship as the potential difference between anode and the cathode.

The various parts of the apparatus are also arranged and proportioned so that when the track section is unoccupied, the value of the current supplied by the current transformers Al and A2 to the grid transformer ATS is such that the current supplied by the grid transformer to the grid circuit of the tube AVI is suflicient to charge the tube grid 32 with a potential high enough to render the tube conducting.

Accordingly, on the supply of this potential to the grid 32 of the tube AVI, during the halfwave periods in which the polarity of the current in the circuit to which current is supplied by the secondary winding 42 of the transformer ATI is such that the anode 33 of the tube AVI is positive with respect to the cathode 34, current flows from the anode to the cathode, thereby effecting the flow of current in the circuit of the winding of the relay AREI.

The flow of current from the anode 33 to the cathode 34 is interrupted during the half-wave periods in which the anode is negative with respect to the cathode. However, on subsequent reversal of the polarity of the current supplied by the secondary 42, the tube AVI is again rendered conducting, provided the grid potential has been maintained at the proper value. The winding of the relay AREI, therefore, is supplied with pulsating unidirectional current as long as the grid potential is maintained. On this supply of unidirectional current the winding of the relay is energized and the movable contacts of the relay are held in their picked up positions.

When the grid potential is reduced the tube. becomes non-conducting and the supply of current to the winding of the relay AREI is interrupted with the result that the movable contacts of the relay AREI are released.

When a train is present in the track section and reaches a point at the right of the station A, the wheels and axles of the vehicles forming the train provide a shunt path between the track rails so that alternating current supplied to the track rails by the track transformer ITRA may flow between the track rails through this shunt path, and does not flow in the portion of the: track rails with which the current transformers AI an A2 are associated. These transformers, therefore, will not supply current to maintain the grid potential of the tube AVI, and the tube will be rendered non-conducting while, the relay AREI will be deenergized.

The relay AREI has a movable contact 45, which, when picked up, establishes the circuit through the wire 20 through which a connection is established from one terminal of the winding 5 of the interlocking relay K to a branch of the wire 44 and thereby to the terminal BX of the source of alternating current. When the relay AREI is released the contact 45 is open, thereby interrupting the supply of current 'through this contact and the wire 20, and thereby to the winding 5 of the interlocking relay K. On this interruption of the supply of current to the winding 5, the relay X will initiate operation of the crossing signal S unless the supply of current to the relay winding is established by other means.

The equipment associated with the station A includes timing means for establishing a connection independent of the relay AREI between the wire 20 and the wire I 4 and thereby with the terminal BX if the time required for a train to traverse the distance from the entrance end of the track section to the station A exceeds a predetermined period.

associated with station A includes an electronic tube AV2, a relay ARE2, and a condenser AC4. The tube AV2 is of a type having a pair of electrodes 41. and 48 mounted in' a sealed envelope filled with an inert gas at a suitable pressure. The tube AV2 is of such character that it is non-conducting until the potential impressed across its terminals exceeds a critical value, while it remains conducting until this potential is reduced substantially below the critical value, whereupon'it again becomes non-conducting.

The timing means includes a transformer AT2 having one terminal of its primary winding 56 connected by way of a wire 5| with a branch of the wire I2, and thereby with the terminal CX of the source of alternating current. This circuit of wire 5| is controlled by acontact 52 of the relay ARE2. When the contact 52 is in its released position it connects the wire 5| directly to a branch of the wire l2, while when the contact 52 is in its picked up position it connects the wire 5| to a wire '53 which is connected to the wire I2 by a contact 54 of the relay AREI when that contact is picked up.

The other terminal of the primarywinding of the transformer AT2 is connected by way of a wire 55 with a movable contact 56 of the relay AREl. When the contact 56 is picked up it connects the wire 55 to a wire 51 which is connected to the movable contact 58 of the track vrelay ITR. When the track relay ITR is deenergized its contact 58 .is released and connects the wire 51 to a branch of the wire I4 and thereby to the terminal BX of the source of alternating current. When the contact of the track relay lTR is released and the contact of relay AREI is picked up one terminal of the primary winding 50 of the transformer AT2 is connected to the terminal BX of the source of alternating current, while the other terminal of the winding 50 is connected to the terminal CX of the source of alternating current when the contact of relay ARE2 is released, or when the contact of relay ARE2 is picked up provided that the contact of relay AREI is also picked up.

The secondary winding 60 of the transformer AT2 is connected to the input terminals of a rectifier unit ARXl. One of the output terminals of the rectifier unit is directly connected to one side of the condenser AC4, while the other output terminal of the rectifier unit is connected in series with a resistor AR3 to the other side of the condenser AC4. A bridging resistor AR4 is shunted across the terminals of the condenser AC4, while a discharge resistor AR5 is provided and is constantly connected by a wire 62 with one side of the condenser AC4. The other terminal of the resistor AR5 is connected by a wire 63 with a stationary contact which is engaged by a movable contact 64 ,of the relay AREI when the contact is released. The contact 64 is constantly connected by a wire 65 with the side of the condenser AC4 other than that to which the wire 62 is connected. When the contact 64 of relay AREI is released, therefore, the discharge resistor AR5 is connected across the terminals of the condenser AC4 to discharge the. condenser, while the discharge of the condenser is aided by the bridging resistor AR4.

The electrode 41 of the tube AV2 is connected to one side of the condenser AC4, and thus through the resistor AR3 to one of the output terminals of the rectifier ARXI, while the other electrode 48 of the tube AV2 is connected to one terminal of the winding of the relay ARE2. The other terminal of the winding of the relay ARE2 is connected to th wire 62, and thereby to the other output terminal of the rectifier ARXI and also to the other terminal of the condenser AC4.

The winding of the relay ARE2 being connected in series with the tube AV2 is maintained deenergized until the potential impressed on the tube is great enough to cause the tube to b rendered conducting, whereupon the relay winding is energized and the contacts of'the relay are picked up.

The relay ARE2 has associated therewith means operative when the relay becomes picked up at a time when the relay AREI is released to establish a stick circuit to supply current to its own winding to maintain it picked up.

This means comprises a suitable source of supply of direct current which, as shown in the drawings, consists of a rectifier unit ARX2 which is supplied with current from the wires l2 and l4 by a transformer AT3. One of the output terminals of the rectifier ARX2 is connected to the wire 62, and thereby to one terminal of the winding of the relay ARE2. The other terminal of the rectifier unit ARXZ has connected thereto' a wire 68 leading to a back point of contact of movable contact 69 of the relay AREI. The contact 69 is connected by a wire 10 to a front point of contact of movable contact ll of relay ARE2, while the contact II is connected to a terminal of the winding of relay ARE2.

When the relay ARE2 is picked up and the winding is constantly connected by the wire 62 to the other terminal of the rectifier unit. Un-

.der these conditions the winding of the relay ARE2 will be energized by current supplied by the rectifier unit ARX2, and will remain picked up so long as this current supply is maintained.

The relay ARE2 has associated therewith means operative in the event that the relay becomes picked up before the relay AREI releases to establish a circuit shunting the resistance AR3 for supplying current from the rectifier unit ARXl to the tube AV2 to thereby assist in maintaining the relay picked up. Referring to the drawings, it will be seen that a wire I4 is connected in series with a resistor AR6 with the conductor leading from one terminal of the rectifier unit ARXI at a point on said conductor intermediate the rectifier terminal and the resistance AR3. The wire 14 is connected to the movable contact 15 of the relay ARE2. When the contact 15 is picked up it engages a stationary contact to which is connected 9. wire 16 which is also connectedto a stationary contact which is engaged by the movable contact 64 of the relay ARE! when that contact is picked up. The contact 64 is connected by way of the wire 65 with the electrode 4'! of the tube AV2.

It will be seen, therefore, that when the contacts of both relays AREI and ARE 2 are picked up, a circuit which shunts the resistance ABS is established from the rectifier to the tube AV2. Current supplied by the rectifier ARXI is accordingly supplied to the tube AV2 and also to the condenser AC4, with the result that the tube AV2 continues to be conducting, while adequate at station A, except that .the prefix A has been current is supplied to the winding of the relay AREZ to maintain the relay picked up. The resistor AR6 limits the current supplied through this circuit to .a value sufficient to maintain the tube AV2 conducting once it has been started, but insuflicient to cause the tube if not conducting tolbreak down and become conducting.

Operation of timing means On the supply of current to the primary winding 50 of the transformer AT2, current is supplied by the transformer secondary winding 60 to the input terminals of the rectifier unit ARXI, while current from the rectifier output terminals is supplied through the resistance AR3 to the opposite sides of the condenser AC4. .In addition, one output terminal of the rectifier unit ARXI is connected through the resistance AR3 to the electrode 41 of the tube AVZ, while theother output terminal of the rectifier unit is connected by the wire 62 and the winding of the relay ARE2 with the electrode 48 of the tube AVZ.

On the initial supply of current from the output terminals of the rectifier unit, the condenser AC4, being substantially without charge, absorbs the current supplied through the resistance AR3,

with the result that the difference in potential at the two sides of the condenser is relatively small, while the difference in potential between the electrodes 4'! and 48 of the tube AVZ, which are connected in parallel with the sides of the condenser AC3, is likewise relatively small. At this time the difference in potential between the electrodes 41 and 4B of the tube is less than the breakdown value of the tube with the result that current does not flow between the tube electrodes, .and therefore does not fiow through the winding of the relay AREZ so the contacts of the relay AREZ remain in their released position.

As a result of the supply of current to the opposite sides of the condenser AC4 the potential difference between the two sides of the condenser is increased. while there is a corresponding increase in the difference in potential between the electrodes 41 and 48 of the tube AV2.

After current has been supplied to the condenser AC4 for .a predetermined time interval, the potential difference built up between the sides of the condenser, and also between the electrodes of the tube AV2, is increased to a value exceeding the breakdown value of the tube AV2, whereupon current flows between the electrodes 41 and 48 of the tube and also through thewinding of the relay AREZ causing the contacts of the relay AREZ to bepicked up.

Itwill be seen, therefore, that on the supply of current to the transformer AT2, the relay AREZ does not pick up instantaneously. Instead the operation of the relay is delayed for a period of time determined by that required to build up a potential difference between the sides of the condenser AC4 equal to the breakdown value of the tube AVZ.

Apparatus associated with stations 15' and C tions B and C is identified by the same reference characters as are employed for the apparatus replaced by the prefix B or C. The construction and operation of the apparatus associated with the stations B and C are the same as the corresponding apparatus at station A and need not be described in detail.

The stations A, B and C are located at spaced points throughout the track section IT. The station A is spaced from the intersection H a distance such that if a train is approaching the intersection at a relatively high speed, as for instance in excess of 30 miles an hour, the highway crossing signal S should be started in operation when the train reaches the station A in order togive users of the highway proper warning of the approach of the train.

The station B is spaced from the intersection H a distance such that when a train is approaching the intersection H at a medium speed, as for instance at a speed less than 30 miles an hour, but greater than 20 miles an hour, operation of the crossing signal S should be initiated when the train reaches that station but not sooner.

Similarly, station C is spaced from the intersection H a distance such that if a train isappreaching the intersection at a low speed, as for instance less than 20 miles an hour, the crossing signal S should be started to operate when the train reaches that station but not sooner.

The station C is located far enough from the intersection H so that if a train passes station B without initiating operation of the crossing signal, and then increases its speed, the crossing signal S, if started in operation when the train reaches station C, will operate for a sufficient period of time before the train reaches the intersection.

Operation of system The operation of the system as a whole will now be described. It is assumed in this description that the track sections IT .and 2T are both unoccupied, that the signal S is deenergized, that the windings of the interlocking relay K are both energized, and that the other apparatus is in the condition which it normally assumes when the track section is unoccupied.

Alternating current supplied from the terminals BX and CK of the source of alternating current supply flows through the wires l4 and I2 to the primary winding l5 of the track transformer ITRA and to the local winding IU of the track relay TR. On the supply of current to the primary winding l5 of the track transformer I TRA, current is supplied from one terminal of the secondary winding I6 to one of the track rails through which it flows to the other end of the track section, thence through the control winding 9 of the track relay TR, and through the other track rail to the other terminal of the secondary winding of the track transformer I'IR. The flow of current in this circuit is limited in the usual manner by the impedance I! to prevent excessive current flow when the section is occupied.

On the supply of alternating current to both the local and the control windings of the track relay TR the movable contact 58 of this relay is held in its picked up position, thereby interrupting the circuit through the primary winding 50 of the transformer ATZ of the timing means located at station A.

On the flow of alternating current through the track rails I and 2, the current transformers Al and A2, BI and B2, and Cl and C2 associated of which is connected to the terminal CX of thewith the stations A, B, and C, respectively, supply current to the grid transformers at those stations to maintain the potential on the tube grids at a value high enough to cause these tubes tobe conducting. Accordingly the windings of the relays AREI, BREI and CREI are energized and the movable contacts of these relays are held in their picked up positions.

Eachof the relays AREI, BREI and CREI has a contact 45 controlling the circuit through the wire 20 leading to one terminal of the winding 5 of the interlocking relay K, the other terminal source of alternating current. When all of the contacts 45 are in their picked up positions a circuit is established from the winding 5 to a branch of the wire I4, and thereby to the terminal BX of the source of alternating current.

The winding 5 of relay K being energized holds the con-tact I in its picked up position, while the winding 6, being also energized by the circuit (not shown) associated with track section 2T, holds the contact 8 picked up with the result that the circuit to the signal S is interrupted.

At this time the relays ARE2 and BREZ are both deenergized, while the condensers AC4 and Operation of system on passage of a slow train A train traveling from left to right in the track stretch will enter the section IT at the left-hand end. As soon as the train enters the track section IT the wheels and axles of the vehicles comprising the train provide a circuit between he track rails shunting the control winding 9 of the track relay I'I'R, thereby de rgizing the windingil.

On deenergization of the winding 9 of the rack relay I'I'R the contact 58 thereof drops to is released position and engages its back conact, thereby establishing a circuit from 'the'wire l4 to wire 51 leading to one terminal of the transformer AT2 at .station A. As the relay AREI is energized and its contact 56 is picked up, Wire 51 is connected to a terminal of primary winding of transformer AT2. At this time the other terminal of the primary winding of transformer. AT2 is connected to the wire l2 by the wire 5| and contact 52 of relay ARE2.

The circuit from the source of alternating current to the primary winding of transformer ATZ b'eing complete as soon as the contact of relay i TR becomes released, the transformer A'I2 supplies current to the rectifier ARXI which in turn supplies current to charge the condenser AC4. As soon, therefore, as a train enters the section IT charging of the condenser AC4 of the. timing means at station A is started and continues as the train advances in the track ection towards station A.

Station A is located a substantial distance from the entrance end of the track section IT and an appreciable period of time is required for a train to traverse the distance from the end of the track section to station A. The time required for the train to traverse this distance varies, of course, with the speed of the train.

The distance from the end of the track section to the station A, the capacity of the condenser AC4, the value of resistance AR3, the breakdown value of the tube AV2, and the values of other portions of the apparatus are selected and proportioned so that the difference in potential developed between the two sides of the condenser will build up to a value in excess of the breakdown value of the tube AV2 before the train reaches station A if the train is traveling at a rate slower than 30 miles an hour, but so that the potential developed between the sides of the condenser AC4 will not be build up to the 'break- 6 down value of the tube AV2 before the train reaches station A if the train is traveling at a speed in excess of 30 miles an hour.

Since, therefore, the train is assumed to be traveling at a speed less than 30 miles per hour, the tube AV2 will be rendered conducting before the train reaches station A. When'the tube AV2 breaks down current flows through the winding of the relay ARE2 causing the movable contacts of this relay to be picked up. 15

When the contact 82 of the relay ARE2 is picked up a circuit is established through the contact 82 and a wire 8-3 to connect the wire 20 to a branch of the wire l4, and thereby to the terminal BX of the source of alternating current. Accordingly, on subsequent deenergization of the relay AREI and opening of its contact 45, the supply of alternating current to the winding 5 of the interlocking relay K will not be interrupted and the relay K will not start the'crossing signal S in operation.

As the relay ARE2 is energized before the train reaches station A, and, therefore, while the contacts of relay AREI are still picked up, a circuit which may be identified asthe first stick circuit is established which shunts the resistor AR3, to thereby increase the current supplied to the winding of the relay AREZ and insure that its cludes resistance ARE and wire 14 leading from 35 one output terminal of the rectifier unit ARXI, contact of relay ARE2, wire 16, contact 64 of relay AREI, and wire 65. This first stick circuit has the resistance AR6 interposed therein which limits the current supplied to the tube AV2 to a value sufllcient to maintain conductivity of the tube, but not sufllcient to cause the tube to break down and become conducting if the flow of current through the tube, is not already established.

As the relay ARE2 remains energized the connection of the wire 20 to the branch of the wire I4 is maintained. I

In addition, when the winding of the relay ARE2 is energized the movable contact 52 is moved out of engagement with its back point of contact and into engagement with its front point of contact, thereby transferring the connection of the wire 5|, leading from the primary winding 50 of the transformer AT2, to the branch of the 55 wire 12 by the wire 53 and the contact 54 of the relay AREI.

As the train proceeds from left to right in the track section IT, it will reach and pass the point at which the current transformers, Al and A2 are located, and the wheels and axles of the vehicle of the train will provide a shunt path oetween the rails so that substantially no current will flow in the portions of the track rails l and U 2 adjacent the current transformers Al and A2. 65

The transformers Al and A2, therefore, will no longer supply current to the grid transformer ATS, while the grid transformer will no longer supply current to maintain the potential on the grid 32 of the tube AVI. The tube AVI, there- 70 fore, will be rendered non-conducting and the supply of unidirectional current to the windin of the relay AREI will be interrupted, with the result that the contacts of the relay ARE! will be opened. 78

tent through the rectifier unit ARXI.

On deenergization of the relay AREI the contact 45 of this relay is opened, but its opening is without consequence as a circuit from the wire I4 to the wire 2|] was established when the relay ARE2 was energized.

On deenergization of the relay AREI, the contact 64 closes, thereby completing a circuit for the winding of the relay AREZ which was partially established when the contact 'II of relay AREZ was picked up. This circuit may be identified as the second stick circuit and supplies current from the rectifier unit ARX2 to the winding of the relay AREZ to maintain this relay energized until the relay AREI is again energized.

In addition, on deenergization of the relay AREI the circuit of the primary winding 50 of the transformer ATZ is interrupted by the opening of contacts 56 and 54, and current, therefore, is no longer supplied by the rectifier unit ARXI to the condenser AC4 nor to the first stick circuit, and thus through the tube AV2 to the winding of the relay ARE2. The relay AREZ, however, remains energized by current supplie through the second stick circuit.

On deenergization of the relay AREI the contact 64 drops out of engagement with its front point of contact, thereby interrupting the first stick circuit. When the contact 64 engages its back point of contact, it completes a circuit between opposite sides of the condenser AC4 through the resistance AR5, this circuit being traced from one terminal of the condenser AC4 through wire 65, contact 64, wire 63, resistor AR5 and wire 62 to the other terminal of the condenser AC4. This circuit provides means for dissipating any charge on the condenser AC4. The discharge of the condenser AC4 may also take place through the resistors AR3 and AR4, and to a limited ex- Accordingly, when the contacts of relay AREI are released the charge on the condenser AC4 is quickly dissipated so that the condenser is ready for another cycle of operation.

On the deencrgization of the relay AREI the contact 80 closes, thereby connecting a branch of the wire I4 to the wire 51 leading from station A to the primary winding of the transformer B'IZ of the timing means at station B. The relay BREI is assumed to be energized at this time with the result that its contact 56 is closed to connect wire 51 to the terminal of the transformer primary winding, while the other terminal of this transformer winding is connected to the wire I2 at this time. Accordingly, on closing of the contact 80 of filay AREI- at station A, which occurs as soon as the train advances in the track section to station A, the circuit through the primary winding of the transformer BT2 at station B is completed and this transformer supplies current to the rectifier unit BRXI associated therewith, and the timing means at station B begins to measure the time required for the train to traverse the distance from station A to station B, to thereby determine whether the operation of the crossing signal S should be initiated when the train reaches station B or should be delayed until the train reaches station C.

As pointed out above, it is assumed that the train is traveling at a slow speed, that is, less than 20 miles an hour. The time required for the train to traverse the distance from station A to station B is such that the difference in potential developed between the sides of the condenser BC4 at station B will exceed the breakdown value of the tube AVZ before the train reaches station E, and the timing means at station B will operate in the manner described in detail in connection with station A to establish a circuit from the wire l4 to the wire 20'before the contact 45 of relay AREI is released to interrupt the circuit controlled by it between the wire 20 and the wire I4.

Accordingly, when the train reaches station B and shunts the current in the track rails away from the current transformers BI and B2 at station B and causes deenergization of the relay BREI, the circuit to the winding 5 of the interlocking relay K is not broken and the relay K will not initiate operation of the signal S.

The equipment at station C does not include timing means as it is unnecessary to measure the speed of the train traveling from station B to station C since it is desired that operation of the crossing signal S be started when the train On deenergization of the winding5 the contact 1 is released and completes the circuit to the crossing signal S, which thereupon operates to warn users of the highway of the approach of a train.

On movement of the train into the track section 2T, the apparatus (not shown) associated with that section operates to interrupt the circuit to the winding 6 of relay K. Because of the internal construction of the relay K, on dee ergization of winding 6 at a time when winding 5 is deenergized and contact 1 is released, the contact 8 will not release to complete the circuit to the crossing signal S. Instead the contact 8 will be held in the open position and will remain in the open position on subsequent energization of the winding 5 and picking up of the contact 'I occasioned by movement of a train out of track section IT. The contact 8 will be held in the open position following the picking up of contact 1 until the winding 6 is again energized which terminates control of the contact 8 by the contact I. Thereafter contact 8 is held in the open position due to energization of the winding 6, but will drop to the closed position on subsequent deenenergization of the winding 6 while the winding 5 is energized.

Accordingly when the train vacates the track section IT and the winding 5 is again energized, the interlocking relay K operates to cut on operation of the signal S.

As long as any part of the train is present in track section IT a shunt path between the track rails is provided and little or no current flows through the rails I and 2 at stations A, B and C. Accordingly the current transformers at these stationsdo not supply current to establish the grid potential necessary to render the tubes AVI, BVI and CVI conducting. The relays AREI, BREIv and CREI, therefore, remain released, while the relays ARE2 and BREZ remain energized. In addition the relay ITR remains released.

When the train vacates track section IT the shunt path between the track rails is, removed and current supplied by the track transformer I'IRA again flows through the track rails l and 2 the entire length of the track section and energizes the control winding 9 of the track relay ITR, causing the contact 58 thereof to be picked up, thereby preventing the supply of current to transformer ATZ on energization of relay AREI.

In addition as a result of the flo'w'of current through the track rails the current transformers at stations A, B and supply current to establish the grid potential on the tubes AVI, BV! and CVI and render these tubes conducting. When these tubes become conducting the relays AREI, BREI and CREI are energized and pick the circuit from wire l4 to line 20, while its contact ll interrupts the second stick circuit at another point. In addition, on the release of relay AREZ the contact I interrupts the first stick circuit for the relay AREI, while the contact 52 moves into engagement with its back point contact.

On energization of the winding of relay AREI contact 80 thereof is picked up to interrupt the supply of current to transformer BTZ at station B on energization of relay BRE2, while the contact 64 of relay AREI is picked up to open the circuit through the resistor AR5. In addition, the contact 54 is picked up. 1

The various parts of the timing means associated withstation A are accordingly restored to the initial condition and the timing means is ready for another cycle of operation.

The timing means and the train detecting means associated with station 13 operate atthis time in. the same manner as that associated with station A, and the apparatus associated with the 7 track section IT is conditioned to respond to the passage of another train.

Operation of system on passage of a fast train The operation of the system in response to the passage of a slow train having been described, the operation of the system in response to passage of a fast train will now be described.

On entrance of a fast train into the track section IT from the' left, the track relay I'I'R..is released as before, and the circuit to the primary winding 50 of the transformer AT! is completed. Current, therefore, will be supplied. by the rec'- tifler unit ARXI through the resistor AR3 to the condenser AC4. I

As the train is traveling at a rapid rate, as for instance in excess of 30 miles per hour, the time required for the train to traverse the distance from the entrance of the track section to station A is less than that required to build up the difference in potential on opposite sides of the condenser AC4 to a value great enough to cause the tube AV2 to break down and become conducting.

Accordingly the relay ARE? will still be released when the train reaches station A and effects operation of the train detecting means at that station to cause the relay AREI to be released.

.On release of relay AREI before the relay AREZ has become energized, the contact 45 of the relay AREI is opened, thereby cutting off the connection from wire 20 to wire l4. As the relay ARE! is still released there is no circuit between the wire 20 and the wire l4 through the contact 82 of the relay AREZ. Accordingly, the circuit through the winding 5 of the interlocking relay K is interrupted and the movable contact I of relay K is released, thereby completing the circuit to the signal S and initiating operation of the signal.

It will be seen, therefore, that on movement of a fast train through the track stretch, operation of the crossing signal is initiated as soon as the train reaches station A, which is far enough removed from the highway intersection to cause the signal to be operated for the proper interval of time before the train reaches the highway crossing, even though the train is traveling at a high rate of speed.

0n the release of the relay ARE! prior to energization of the relay ARE2 the contact 55 of the relay AREI is opened, thereby cutting off the supply of energy to the transformer AT! with the result that current is no longer supplied to increase the potential difference between the two sides of the condenser AC4, which, as

previously stated, was insuflicient to render the be discharged, by flow of current through the resistor AR5, as well as by flow through the resistors AR3 and AR4. The charge on the condenser AC4 wlll be quickly and completely dissipated so that on the subsequent supply of current to the condenser the time required to build up the potential difierence between the sides of the condenser will not be reduced by the presence of a partial charge on the condenser.

0n the releaseof the relay AREI the contact 80 thereof is closed, thereby establishing connection from a branch of the wire l4 .to the wire 51 leading to the transformer BTI at station B. At this time the relay BREI of the train detecting means at station B is energized, and its contact 55 completesthe circuit from wire 51 to transformer 3T2 so that when the contact 80 of relay AREI closes current is supplied to the primary winding of transformer 3T2.

cordingly the charge on the condenser AC4 may tion 18 will be operated as described in connecinterrupt the circuit through the wire 20, while the relay BRE2 will not be operated to establish connection from the wire M to the wire 20, and the winding of the interlocking relay K will continue to be deenergized and effect operation of the signal S.

At the time of the opening of the contact 45 of relay BREI, the circuit through the wire 20 was already interrupted at the contact 45 of the relay ARE] so the deenergization of relay BREI was without consequence since the winding of interlocking relay K was already deenergized.

Similarly when the train reaches station C the relay CREI is deenergized and its contact 45 interrupts the circuit through the Wire 20 at another point.

When the train advances into track section 2T the equipment (not shown) associated with that section is operated to interrupt the circuit through the winding 5 of the interlocking relay K, but because of the internal construction of the relay K, the contact 8 will not drop to its closed position.

When the rear of the train vacates the track section IT the shunt path between the track rails provided by the wheels and axles of the vehicles comprising the train is no longer present. Accordingly the current supplied by the track transformer ITRA again flows the entire length of the track rails of the track section IT with the result that the track relay ITR becomes picked up, while the relays AREI, BREI and CREI also are again energized and the apparatus is conditioned to respond. to the passage of another train through the track stretch.

The operation of the system in response to the passage of a slow train and of a fast train having been explained, the operation of the system on the passage of a train of medium speed, that is at a speed below 30 miles an hour but above 20 miles an hour, will now be explained.

Operation of system on passage of a train at medium speed On entrance of the train into the track section IT from the left, the track relay ITR will be deenergized as before, and the contact 58 will complete the circuit through the wire 51 to the timing means at station A. The condenser AC4 will have current supplied thereto, and since the train is assumed to be traveling at medium speed, the potential between the two sides of the condenser will be built up to a value exceeding the breakdown value of the tube AV2 before the train reaches station A.

Accordingly the relay AREZ will be energized and its contact 82 will establish a circuit from the wire l4 to the wire 20 before contact 45 of the relay AREI is released to interrupt the circuit betweenthe wires I4 and 20 which it controls. The supply of current to the winding 5 of the interlocking relay K will be maintained, and operation of the signal S will not be initiated until the train advances farther into the track section.

On the release of relay AREI the circuit through the wire 51 to the transformer BTZ ,of the timing means at station B is completed and the supply of current to the condenser B04 is started. The distance between the stations A and B is such that a train traveling at a med um speed will traverse the distance between the stations A and B before the, condenser BC4 is charged to a value high enough to cause the tube BVZ to break down and become conduct- Accordingly the train will reach station B and rent to maintain their grid potential.

cause deenergization of relay BREI before the relay BREZ has become energized. On this deenergization of the relay BREI its contact 45 interrupts the circuit through the wire 20 to the interlocking relay K with the result that the winding 5 of relay K is deenergized and contact I becomes released to initiate operation of the signal S, while the supply of current to the condenser BC4 is interrupted and a circuit through the resistance BB5 is established to dissipate the charge built up on the condenser.

It will be seen, therefore, that on the passage of a train of medium speed through the track section the crossing signal S will be maintained inoperative until the train reaches station B, whereupon operation of the signal will be initiated.

Operation of system during movement of train in reverse direction The system provided by my invention is arranged so that on movement of a train through the track stretch in the reverse direction, that is from right to left, the equipment associated with the track section will be automatically restored to its normal condition on departure of the train from the track section.

If a train is traveling in the track stretch from right to left, the equipment (not shown) associated with section 2T will be operated as described above in connection with the apparatus associated with section IT to interrupt the circuit to the winding 6 of the relay K so that this relaywill effect operation of the signal S.

On entrance of the train into track section IT, a shunt path between the track rails is provided with the result that the track relay ITR, is deenergized, while the tubes AVI, BVI and CVI of the train detecting means at stations A, B and C are rendered non-conducting because of the interruption of the supply of our- The relays AREI, BREI and CREI, therefore, are de energized and the circuit through the wire 20 to the winding5 of the relay K is interrupted by each of these relays.

In addition on release of contacts 56 of relays AREI and BREI, the circuits of the primary windings of transformers AT2 and BTZ are interrupted and no current will be supplied to the condensers AC4 and B04.

Because of the internal construction of the relay- K, on this deenergization of the winding 5 ate time when the winding 6 is deenergized, the contact 1 does not drop to its closed position, but is held in its open position.

As the train proceeds through the track stretch the rear of the train will successively pass the stations C, B and A. When the rear of the train is located at the left of station C, current supplied by the transformer ITRA again flows through the portions of the track rails I and '2 on which are mounted the current transformers Cl and C2, with the result that the grid potential of the tube CVI is reestablished and this tube is again rendered conducting. The relay CREI will, therefore, be energized and the contact 45 will be closed.

Similarly, when the train has progressed to a point at which the rear of the train is located at the left of the station B, the tube at that station will be rendered conducting and the relay BREI will be energized and its contact 45 will be closed, while its contact 56 will also be closed. At this time, the relay AREI being deenergized and its contact 80 being closed, closure of contact 56 of relay BREI completes the circuit to the transformer BT2 of the timing means at station B with the result that current is supplied to the condenser BC.

If the train is traveling slowly, or should stop before the rear of the train has advanced to a point at the left of station A, the condenser 1304 will be charged to a value exceeding the breakdown value of tube BV! and this tube will be rendered conducting and will cause the relay BREI to be energized. On this energization of the relay BRE2, the contact 82 thereof is closed and completes a circuit from wire I4 to wire 20, and thence to the winding 5 of the interlocking relay K. On this energization of the relay BREZ at a time when the relay BREI is energized, the first stick circuit for the winding of relay BRE2 is established. This circuit includes resistance BRILwire I4, contact I5, wire I6, contact 64, and wire 65. At this time as the relay BREI is energized the second stick circuit for the relay BRE2, that is the circuit through which current, is supplied from rectifier BRX2, is not completed.

On further movement of the train so that the rear of the train is located at the left of the station A, the relay AREI becomes energized, with the result that its contact 56 closes and completes the circuit to the transformer AT2, while the contact 80 is picked up and opens the circuit to the primary winding of the transformer BT2 at station B. In addition, the contact 45 of relay AREI is closed, thereby establishing connection from the wire I4 to the wire 20, so that the circuit through the winding 5 of interlocking relay K is maintained after relay BREZ releases.

When the relay ARE I picks up and interrupts the circuit to the primary winding of transformer BT2 the supply of current by that transformer to the rectifier unit BRXI is cut oil. The supply of current from the rectifier unit to the first stick circuit for the winding of relay BRE! is likewise cut off and the relay BREZ releases, thereby breaking the stick circuit, while the contact 82 opens to interrupt the connection which it establishes between the wires I4 and 20. However, before this occurs a connection between these wires is established by the contact 45 of relay AREI so that the supply of current to the winding 5 of interlocking relay K is maintained.

If the train is moving slowly while the rear of the train is in the section between station A and the left-hand end of track section IT, or if the train should stop while the rear of the train is in this portion of the track section, the timing means associated with station A will operate in the manner described in connection with station B. When the train passes out of the track section, the track relay ITR picks up, thereby opening the circuit through the primary winding 50 of transformer AT2 with the result that the relay ARE! releases if it has become picked up.

The charge built up in the condensers AC4 and BC is dissipated through the resistors R3 and R4 associated therewith so that on subsequent movement of a trainthrough the track stretch from left to right the timing means associated with stations A and B will accurately measure the speed of the train.

.g It will be seen, therefore, that as soon asthe train traveling from right to left passes out of the track section, the equipment for controlling the crossing signal is restored to its normal condition, and islprepared to respond to the passage of a train through the track section fromleft to right.

Operation of system in response to movement of two trains The equipment provided by my invention is arranged in such a manner that-in the event that a train approaching the highway crossing enters the track section before another train traveling in the same direction has vacated the section, the crossing signal will be operated for the proper interval of time beforethe second train reaches the intersection.

As a result of the movement of the first train through the track section IT, it being assumed that the rear of this train remains in the track section, the flow of current in the portions of the track rails at the stations C, B and A is inter-' rupted with the result that the tubes CVI, BVI and AVI -of the train detecting means at these stations are rendered non-conducting. The relays .CREI, BREI and AREI at these stations, therefore, are deenergized and the interlocking relay K is conditloned to eflect operation of the signal S. Q

The relays ARE! and BRE2 associated with timing means at stations A and B may be energized or deenergized depending upon the speed at which the first train was moving when it entered the track section. For purposes of illustration it will be assumed that the first train was traveling at a medium speed with the result that the relay ARE2 is energized, while the relay BRE2 is not energized. v

With the equipment in this condition, and with the rear of the first train located at a point in the track section IT adjacent the intersection H, it will be assumed that a second train travel-' ing from left to right, enters the track section IT. The second train will necessarily be moving at a slow speed when it enters the section IT, since the wayside signal, not shown, at the entrance to this track section or adjacent thereto will indicate that the section is occupied.

At the time the second train enters the track section IT, the track relay ITR. is released due to the presence of a portion of the first train in the track section. The entrance of the second train into the track section, therefore, does not cause any change in the condition of the equipmentassociated with the track section.

It will be assumed that the first train has continued its' movement so that the rear of that train vacates the track section IT after the second train enters the track section IT, but before the second train reaches station A.

In the interval between the time at which the second trainenters and the first train vacates the track section, the tube AVI is non-conducting and the relay AREI is deenergized with the result that contact 56 of relay AREI is open and interrupts the circuit of the primary winding 50 of transformer AT2. Ijhe relay ARE2 is assumed to be energized at this time. Since the relay ARE2 is energized, and the relay AREI is deenergized, the winding of the relay ARE! is supplied with current by the rectifier unit ARX2 through the second stick circuit.

At this time, as the relay ARE! is released, the contact Bl thereof establishes a circuit through the resistance ARE so that any charge which' When the first train vacates the track section thereupon interrupts operation of the crossing signal S.

When the relay AREI picks up, its contact 69 breaks the second stick circuit of the relay ARE! so that the relay ARE! releases.

In addition, on the picking up of relay AREI its contact 56 is closed, thereby completing the circuit to primary winding 50 of the transformer AT! since the track relay I'IR is released due to the presence of the-second train in the I track section. The circuit through the primary, winding of the transformer AT! is completed regardless of whether the relay ARE! is released or is picked up. If the relay ARE! is released, the wire 5| leading from one terminal of the primary winding 50 of transformer AT! is connected by the contact 5! directly to a branch of the wire 1!. If the relay ARE! is picked up, the wire 5| is connected by the contact 5! to the wire 53, which at this time is connected by the contact 54 of the relay AREI to a branch of the wire l2. Accordingly when the relay AREI picks up, current is supplied to the primary winding of the transformer AT!, with the result that current is supplied by the transformer to the rectifier unit ARXI, and by that unit to the condenser AC4. As the charging of the condenser is started promptly on the departure of the first train from the track section, the timing means associated with station A will make the most accurate determination possible of the speed of the second train.

'On the picking up of the relay AREI, if the relay ARE! has not released but has been maintained energized by current supplied by the rectifier ARX! through the second stick circuit, the contact 64 of the relay AREI will complete the 45 first stick circuit for the winding of the relay ARE! to which current is supplied by the rec'- tifier unit ARXl. The flow of current in this circuit is limited by the resistor ABS to a value insuflicient to cause the tube AV! to break down and become conducting. Accordingly the supply of current to this circuit will not effect energization of the relay ARE! and cause the relay to remain picked up. On picking up of relay AREI and interruption of the second stick cir- 55 cuit by its contact 59 the relas AREl will, therefore, release if it has not already released.

"When the relay ARE! releases, its contact 8! opens, thereby breaking the circuit which it controls between the wire' l4 and the wire 20.

When the relay AREI picks ,up, its contact 80 is opened, thereby interrupting the circuit from the wire l4 to the wire 51 leading to the transformer BT!. Accordingly the picking up of contact 56 of relay BREI will not establish a circuit to the transformer BI! and current will not be supplied to the condenser BC4, while the relay BRE!, which was assumed to be deenergized, will remain deenergized.

As the second train advances in the track section, the condenser AC4 is being charged, and

since the second train is traveling relatively slowly, the condenser AC4 will probably be charged to a value high enough to cause the tube AV! to break down and energize the relay ARE! before 75 the train reaches the station A, even though the train had traversed a portion of the distance from the end of the track section to the station A before the charging of the condenser AC4 was begun. If this sequence of operation occurs, and the relay ARE! is energized before the relay AREI is deenergized, the contact 82 of the relay ARE! will close and establish a circuit between the wire l4 and the wire 20 before the contact 45 of the relay AREi opens. Accordingly the circiut to the winding of the interlocking relay K is maintained and operation of the crossing signal S is not started when the train reaches station A and causes deenergization of the relay AREI.

However, as the train continues to advance in w the track section IT, operation of the crossing signal S will be initiated, in the manner heretofore described in detail, when the train reaches station B or C depending upon the speed at which the train is moving.

If the second train is traveling at a relatively rapid rate when it enters the track section IT, or if it is traveling at a relatively slow speed and should advance a substantial part of the distance from the entrance end of track section IT to the station A before the first train vacates the track section and charging of the condenser AC4 at station A is initiated, the second train may reach station A and cause deenergization of the relay AREI before the condenser AC4 is charged up sufliciently to cause the relay ARE! to be energized.

If this sequence of operation occurs, when the relay AREI becomes deenergized its contact 45 opens the circuit to the winding 5 of the interlocking relay K, and the relay K thereupon starts the signal S in operation. The start of the operation of signal S will occur somewhat sooner than is necessary to provide a warning of the proper duration since the relatively slowly moving train will require more time to traverse the distance from station A to the intersection H than is required by the trains which normally initiate operation of the crossing signal when they reach station A. A somewhat longer than normal period of operation of the crossing signal under these conditions is not objectionable, and is preferable to a shorter than normal period of operation of the warning signal.

It will be seen, however, that the applicants system is arranged so that the possibility of operation of the signal for anabnormal period of time is reduced to a minimum. As previously pointed out, when the relay AREI picks up following the departure of the first train from the track section, a circuit is established through the primary winding of the transformer AT! irrespective of whether the relay ARE! has released or is picked up. Accordingly the charging of the condenser AC4 is started promptly on the departure of the first train, with the result that current is supplied to the condenser AC4 for the maximum period of time possible under the circumstances, with the resultant maximum probability that the condenser will be charged suiiiciently to effect energization of the relay ARE! before the second train reaches station A.

Operation of system an entrance of train in track section and subsequent exit of train in opposite direction The system provided by my invention is arranged so that, if a train enters the track section, stops and then departs from the track section at the same end as that at which it entered,

the apparatus comprising the system will automatically restore itself to the proper condition to respond to the passage of another train through the track section.

For the purpose ofillustration it will be assumed that a train enters the track section lT from the left, advances a part of the length of the track section, stops and then departs from the left-hand end of the track section.

When the train enters section IT, the track relay ITR. becomes released and the circuit to transformer ATZ is completed so that charging of the condenser AC4 is started. Since the train is about to stop, it will not be traveling rapidly enough to reach station A before the condenser A04 is charged sufficiently to effect energization of relay ARE2. The relay ARE2, therefore, will maintain the circuit to the interlocking relay K and thereby prevent operation of the crossing signal S if the train advances beyond station A.

If the train passes station A, the relay ARE! will be released and will effect the supply of current to the transformer BT2 to thereby start charging of the condenser B04. If the train stops before reaching station B, the condenser BC4 will become charged up and effect energization of the relay BREZ, while the relay BREI will remain energized with the result that its contact 69 interrupts the second stick circuit for relay BREZ and the relay BRE2 will not be energized by current supplied over this circuit.

On subsequent reverse movement of the train so that the end of the train is located at the left of station A, the relay AREI picks up, thereby cutting off the supply of current to the transformer BTZ. As a result the relay BREZ becomes deenergized, while the charge built up in the condenser BC4 is dissipated through the resistors BB3 and BR4.

When the relay AREI picks up, the supply of current to the transformer AT2 is reestablished and charging of the condenser AC4 is again effected. When the train departs from the track section IT, the track relay ITR is again energized and its contact 58 becomes picked up, thereby interrupting the supply of current to the transformer ATZ with the result that the relay ARE2 becomes released if it became energized, while the charge built upon the condenser AC4 is dissipated through the resistors AR3 and AR4. The equipment associated with track section IT is now in its normal condition. The relays of the train detecting means are energized, while the relays of the timing means are deenergized and result in operation of the crossing signal rather than in the failure of the signal to operate.

If for instance the tube associated with one of the train detecting means should become inoperative for any reason, such as failure of its filament, the relay associated with that tube would be deenergized and would interrupt the circuit to the interlocking relay, thereby causing that relay to effect operation of the crossing signal.

Likewise, if the tube of one of the timing means should be rendered inoperative and failed to become conducting, the relay associated with that tube would remain deenergized and would not of the crossing signal sooner than would occur if the timing means functioned in its normal manner.

' -Furthermore, if the track circuit, the current or grid transformers, the track transformer or the associated apparatus should fail to function as intended, the grid potential on the tubes of the train detecting means would not be maintained. These tubes would thereby be rendered non-conducting with resultant deenergization of the relays controlled thereby and interruption of the circuit to the interlocking relay K.

It will be seen, therefore, that the system incorporates important safety features so that failure of operation of the warning signal as a result of failure of the apparatus of the control system is avoided.

In addition it will be seen that the system is arranged in such a manner that cut sections in the track rails are unnecessary at the various stations at which the train detecting means are located. This is an important advantage, particularly if the system is applied to an electrified railroad where cut sections necessitate expensive impedance bonds to carrythe propulsion current between adjacent sections.

Furthermore, it will be seen that the system provides means responsive to the speed of the train approaching the intersection for determining the point to which the train must advance before operation of the crossing signal is initiated in order that the period of operation of the signal prior to the arrival of the train at the intersection will be substantially the same irrespective of the speed of the train.

Construction and Operation of the modification shoum in Fig. 3 of the drawings In Fig. 3 of the drawings I have shown means for adapting the system shown in Figs. 1A and 1B for use on an electrified railway employing alternating current for propulsion purposes. The modification shown in Fig. 3 incorporates means to prevent the propulsion current flowing in the track rails from causing the current transformer to supply current to the associated grid transformer which might result in the supply of current to the grid of the tube associated with the grid transformer. If this condition arose, the tube might be rendered conducting at a time when it is intended that the tube be non-conducting.

As shown in Fig. 3 of the drawings, a condenser 90 and a reactance 9| are connected in series between the wires leading from the current transformers Al and A2. The values of the condenser 90 and the reactance 9| are chosen with respect to the values of the rest of the circuit so that the condenser and the reactance together with the current transformers Al and A2 form a circuit which is resonant to the 25 cycle propulsion current, but is not resonant to the 60 cycle current supplied to the track rails by the track transformer associated with the crossing signal control apparatus. Accordingly any current induced in the current transformers Al and AZ by the 25 cycle propulsion current will be absorbed by the reactance 9| and the condenser 90, thereby preventing undesired supply of current to the tube grid circuit. The reactance BI and condenser 90, however, will not interfere with the supply of 60 cycle current to the tube grid circuit. The tube, therefore, will be rendered conducting in response to the flow of 60 cycle current in the track rails, but will not be rendered conducting as a result of the flow of 25 cycle propulsion current in the track rails.

Construction and operation of the modification shown in Fig. 4 of thedrawings In Fig. 4 of the drawings I have shown a portion of a system embodying my invention and incorporating a modified form of train detecting means.

The system shown in Fig. 4 of the drawings is the same as that shown in Figs. 1A and 13, except as hereinafter pointed out in detail, and the same reference numerals are employed in Fig. 4 as are employed in Figs. 1A and 13 to designate the structure found in Fig. 4 which is common to the system shown in Figs. 1A and 1B.

The system shown in Fig. 4 of the drawings differs from that shown in Figs. 1A and 1B of the drawings in that the System shown in Fig. 4 necessitates the use of insulated joints in the track rails at the various train detecting stations, and is intended for use in non-electrified territory where alternating current track circuits for controlling the signals are not employed. The system shown in Fig. 4 further differs from that shown in Figs. 1A and 13 as the system shown in Fig. 4 employs a tube of the cold cathode type, while the system shown in Figs. 1A and 13 employs a tube of the hot cathode type.

Referring to Fig. 4 of the drawings, the track rails I and 2 of the track section have insulated joints 3 therein defining one end of the track section IT, while the track rails I and 2 also have insulated joints 3a therein at the station A, as well as at stations Band 0, not shown. The track section IT has associated therewith a track relay I TR of the type employed in the system shown in Figs. 1A and 1B. This relay has a local winding I0, and has a control winding prising a grid 32a, an anode 33a, and a cathode 34a mounted in a sealed envelope filled with an inert gas at a low pressure. The tube AVIa has associated therewith a transformer ATIa, the

primary winding 40a of which is supplied with alternating current from the same source as the track transformer, not shown. The tube AVIa also has associated therewith a relay AREI, one terminal of the winding of which is connected to one terminal of the secondary winding 42a of the transformer ATIa. The other terminal of the .transformer secondary winding 02a is connected to the cathode 34a of the tube AVIa, while the other terminal of the relay winding is connected in series with a resistance AR2 with the anode 33a of the tube AVIa. A condenser AC3 is shunted across the terminals of the relay winding.

The equipment at station A includes a trans- .former ATa ,having a primary winding I00 connected across the track rails I and 2 on the side of the insulated joints 3a at station A adjacent the track transformer, not shown, associated with track section IT. The transformer ATa has a secondary winding IOI connected across the track rails I and 2 on the side of the insulated joints 30 at station A opposite from that on which the primary winding I00 is connected.

The transformer ATa has another secondary winding, indicated at I02, one terminal of which is connected to the anode 33a of the tube AVI a, while the other terminal of the winding I02 is connected in series with a resistor ARIa with the tube grid 32a. A condenser ACZa. is connected between the grid 32a and the cathode 34a.

In operation current supplied by the track transformer, not shown, to the track rails I and 2 flows through the primary winding I00 of the transformer ATa and induces current in the secondary windings IN and I02. Current induced in the secondary winding IN is supplied to the track rails I and 2 at the left of station A and flows through these rails and energizes the control winding 9 of the track relay ITR.

If there are any other train detecting stations, such as those identified at B and C in Figs. 1A and 1B intermediate the station A and the track transformer, the current supplied by the track transformer will be supplied around the insulated joints at these stations through the transformers in the manner described above.

The current in primary winding I00 of transformer ATa also induces current in winding I02 with the result that current is supplied through the resistor ARIa and establishes potential on the grid 22a suflicient to render the tube conducting during the half cycle intervals in which the anode 33a is positive with respect to the cathode 34a. As a result during these half cycle intervals current supplied from one terminal of the winding 42 of the transformer ATIa flows through the winding of the relay AREI, resistance AR2 to the anode 23a, thence to the cathode 34a and to the other terminal of the winding 42. As long as the grid potential is maintained, the tube AVIa will be rendered conducting, and current will flow in the winding of the relay AREI and effect energization of this relay. The relay AREI performs the same function as the corresponding relay in the system shown in Figs. 1A and 1B, controlling the timing means, not shown, and also controlling the wire 20 leading to the interlocking relay, not shown, which controls the crossing signal, not shown.

As long as the track section IT is unoccupied, the flow of current through the track rails is maintained, while the potential on the grid of the tube is maintained with the result that the tube is conducting and the relay AREI is energized.

When a train enters the track section IT from the left, a shunt path is provided between the track rails with resultant deenergization of the track relay ITR and closing of its contact 58 to complete the circuit to the transformer AT2 of the timing means at station A. At this time, the train not having advanced as far as station A, current continues to flow through the track rails at station A with the result that the potential on the grid of the tube AVI a is maintained, while the relay AREI continues to be energized.

When the train advances in the track section IT so that the front of the train is at the right of station A, a shunt path is provided between the track rails I and 2 which diverts current from the primary winding I00 of the transformer ATa.

As a result the secondary winding I02 will not supply" current to maintain the grid potential of the tube AVIa and this tube will be rendered non-conducting and the relay AREI will be deenergized.

The supply of current to the transformer ATa will be cut off as long as any portion of the train remains in the portion of track section IT at the right of station A, and accordingly the relay AREI will be maintained deenergized until the train vacates this portion of the track section, whereupon the relay AREI will again be energized.

The operation of the system of which the train detecting means shown in Fig. 4 forms a part is substantially the same as that of the system shown in Figs. 1A and 1B and need not be repeated.

Construction and operation of the modification shown in Fig. 5 of the drawings In Fig. 5 of the drawings, I have illustrated a portion of a modified form of system embodying my invention. The system shown in this figure is similar to that shown in Figs. 1A and 1B of the drawings as it does not require the use of insulated joints in the track rails at the various train detecting sections, but diifers from the systems shown "in Figs. 1A and 1B and Fig. 4 as it employs a different form of means for securing current from the track rails to maintain the grid potential on the tubes of the train detecting means. This system employs a tube AVIa of the same type employed inthe system shown in Fig. 4.

Referring to Fig. 5 of the drawings, the equipment at station A includes a loop I II) mounted between the track rails I and 2 and having'relatively long side portions located adjacent to the track rails I and 2 and extending substantially parallel thereto so that the loop is in inductive relationship to the track rails. The loop III] is shown as comprising two complete turns, but it will be understood that any suitable number of turns may be employed, and it is contemplated that a substantially larger number of turns will be employed so that an effective inductive coupling will be obtained between the loop and the track rails.

The ends of the loop IIII are connected to the terminals of the primary winding III of the transformer ATb. The secondary winding of the transformer ATb is connected to the elements of the tube AVIa in substantially the same manner that the secondary winding I02 of the transformer ATa of the system shown in Fig. 4 is connected to the tube employed in that system. One terminal of the secondary winding H2 is connected to the anode 33a of the tube AVIa, and the other terminal of the transformer secondary winding H2 is connected through the resistor ARIa to the tube grid 32a.

The other circuits employed in the train detecting means shown in Fig. 5 are substantially the same as the corresponding circuits employed in the system shown in Fig. 4 and will not be traced in detail.

In the operation of the system shown in Fig. 5, as long as the track section IT is unoccupied, current supplied by the track transformer, not shown, fiows through the track rails I and 2 and energizes the control winding 9 of the track relay ITR.

The current flowing through the track rails I and 2 induces current in the loop III) with the result that the loop supplies current to the transformer ATb, which in turn supplies current to maintain the potential on the grid 32a of the tube AVIa to render the tube conducting to effect en-,

' ergizatlon of the relay AREI.

When a train enters the track section IT from the left and advances in the section far enough that the front of the train is located at the right of station A, current no longer flows in the portions of the track rails paralleled by the loop I III. Accordingly current is not induced in the loop, and the potential on the grid 32a of the tube AVIa is not maintained. As a result the tube is no longer conducting and the relay AREI is deenergized.

When the train vacates the track section, current will again flow through the portions of the track rails adjacent the loop III], and the grid potential of the tube AVIa will be restored and the tube will again be conducting and will eflect energization of the relay AREI.

Construction and operation of the modification shoum in Figs. 6 and 7 of the drawings In Figs. 6 and 7, I have illustrated a portion of another form of train detecting means embodying my invention. This form is shown as incorporating a tube AVIa of the cold cathode type, while the modification shown in these figures of the drawings is adapted for use in nontrack circuited territory or where direct current track circuits are employed. This modification does not require the use of insulated joints in the track rails at the various train detecting stations.

The train detecting means shown in Figs. 6 and 7 of the drawings does not require the use of a track transformer to supply current to the track rails in the manner contemplated in the system shown in Figs. 1A and 1B of the drawings. Similarly a highway crossing control system employing train detecting means of the type shown in Figs. 6 and 7 of the drawings does not employ a track relay as is employed in the system shown in Figs. 1A and 1B of the drawings. Instead suitable train detecting means is provided at a point in the track stretch at the left of station A and operative on passage of a train to initiate charging of the condenser incorporated in the timing means, not shown, at station A.

As shown in the drawings, the tube AVIa has its cathode 34a connected to one terminal of the secondary winding 42a of the transformer ATIa, while the other terminal of the transformer secondary winding is connected in series with the Winding of the relay AREIa and a resistor ARIa with the anode 33a of the tube. A condenser AC3 is shunted across the relay winding, while a wire II5 connects one of the track rails, such as the track rail I, with the circuit leading from the tube anode 33a at a point in that circuit intermediate the resistor ARIa and the transformer.

The track rail I has associated therewith a member H6, in the form of a length of angle iron supported on the crossties III by suitable means, such as supports IIB formed of electrically insulating material. The member H6 is disposed adjacent the inner face of the head of the rail I, but is spaced far enough therefrom to enable the wheels of the vehicles traveling on the rail to pass without their flanges engaging the member II6, as is clearly shown in Fig. 7 of the drawings. The member H6 is preferably of such length that it will bridge over the space between adjacent wheels of the same truck of a car.

The member I I6 is connected by a wire I20 with the grid 32a of the tube AVIa, while a condenser AC2a is connected between the grid and the oathode of the tube AVIa.

The member H6 and the track rail I serve as plates of a condenser which is in series with the circuit connecting the tube grid with the transformer secondary winding. The capacity of the condenser formed by the member I I6 and the track rail I is varied when a train passes through the track section and the flanges ot the car wheels extend between the member I I6 and the head of the track rail.

In operation, current supplied by the transformer secondary 42a flows in the circuit provided by the condenser AC3, wire I IS, the condenser formed by the rail I and the member I I6, the wire I20 to which is connected the tube grid, and the condenser AC2a.

The various parts of the apparatus are selected so that their values are such that when the track section is unoccupied, the potential impressed on the grid 32a is such that the tube is non-conducting and the relay is deenergized.

The various parts of the apparatus are also selected so that when the capacity of the condenser formed by the track rail I and the member H6 is increased as a result of the presence of a wheel flange between the member I I6 and the rail head, the potential on the tube grid is such that the tube is conducting. At this time, therefore, the relay AREI a will 'be energized. The contact 45 of this relay is arranged to complete the circuit to the crossing signal when the. relay is deenergized, and to interrupt this circuit when the relay is energized.

When a train travels past station A, therefore, the tube AVIa will be rendered conducting during the periods in which the flange of a car wheel is present between the member H6 and the head of the track rail. At the times when a wheel flange is not present between the member H6 and the track rail, as when the portion of the car between the car trucks is over the member II6, the tube AVIa is rendered non-conducting, but it again becomes conducting as soon as the flange of a car wheel passes between the member H6 and the rail head. During passage of a train, therefore, the tube AVIa is intermittently rendered conducting, while the relay AREIa is periodically energized. The relay AREIa has a slow releasing characteristic so that it will remain picked up somewhat longer than the time intervals between the periods of conductivity of the tube AVIa. During movement of a train past station A, therefore, thg relay AREIa will remain picked up, but it will release promptly as soon as the train passes beyond this point.

The train detecting means shown in this figure of the drawings may be employed in connection when the relay AREIa oi the system shown in Fig. 6 is deenergized.

Construction and operation of the modification shown in Fig. 8 of the drawings In Fig. 8 of the drawings I have illustrated still another modification embodying my invention. The equipment shown in Fig. 8 is similar to that shown in Figs. 6 and 7, and does not necessitate the use of insulated joints in the track rails at the train detecting station. Neither does this equipment require current to be supplied to the track rails by a track transformer, nor does it contemplate the use of a track relay such as is used in the system shown in Figs. 1A and 1B of the drawings.

The system shown in Fig. 8 employs a transformer I25 mounted between the track rails. The transformer I25 has a generally U-shaped core I26 formed of suitable magnetic material. The arms of the core I26 have elongated head pieces extending parallel to the track rail. The

core I26 is supported from the crossties by suitable means, not shown, so that the head pieces of the core are disposed adjacent to the inner face of the head of the track rail I, but far enough away from the rail head to permit the flanges of the car wheels to pass freely between the core and the rail head. The adjacent ends of the head pieces are spaced apart a substantial distance so that an air gap of sufficient width is present between them to substantially prevent flow of magnetic flux directly across this space.

One arm of the core I26 has the primary winding I28 mounted thereon. This winding is connected to the branches of the wires I2 and I4, and thereby to the same source of alternating current as the primary winding 40a of the transformer A'IIa.

The other arm of the core I26 has the secondary winding I30 mounted thereon. One terminal of the secondary winding I30 is connected to the grid 32a of the tube AVIa, while the other terminal of the Winding I30 is connected in series with a resistor ARIa with the tube anode 33a.

The current supplied to the winding I 28 creates magnetic fiux in the core I 26. Because of the large air gap between the head pieces of the core and between the head pieces and the track rail, the permeability of the magnetic circuit of which the core I26 forms a part is relatively poor. Accordingly on energization of the primary winding I28 little current is induced in the secondary ,winding I30 with the result that this winding supplies little current to the tube grid circuit.

When a train passes over the portion of the track stretch at station A, the presence of the flange of a car wheel between the core I26 and the rail I increases the permeability of the magnetic circuit of which the core forms a part. Similarly, the presence of the heavy iron parts of the car truck above the core I26 provides a magnetic path bridging the gap between the head pieces of the core I26 and thereby increases the permeability of the magnetic path of which the core forms a part. As a result of these increases in the permeability of the magnetic path through the core I26, more current is induced in the secondary winding I30 and there is an increase in the current supplied to the tube, grid circuit.

The various parts of the system are selected so that their values are such that when the track stretch is unoccupied, the current supplied by the secondary winding I30 to the tube grid circuit is insumcient to render the tube conducting. At these times, therefore, the relay AREIa will be deenergized.

The various parts of the system are also selected so that their values are such that when the track stretch is occupied and vehicle trucks are passing over the transformer I25, the current supplied by the transformer secondary winding I30 to the tube grid circuit is suflicient to render the tube conducting. The relay AREI a, therefore, will be energized at these times.

, The relay AREIa, like that employed in the system shown in Fig. 6, has a slow releasing characteristic so that it will not become released on momentary interruptions in the supply of current to its winding, with the result that if the tube is momentarily rendered non-conducting during the time between passage of car trucks over the transformer I25, the relay will remain picked up.

Construction and operation of the modification shown in Fig. 9 of the drawings In Fig. 9 of the drawings, 1' have illustrated another form of train detecting means embodying my invention. This system is shown incorporating a tube of the type having a heated filament as its cathode. This system differs from certain of the others in that it requires an insulated Joint in one of the track rails at each train detecting station.

The system shown in this figure of the drawings has an insulated joint 3 in the track rail 2. at the train detecting station A. This system also includes an impedance transformer I having the terminals of its primary winding I 36 connected to the rail '2 on opposite sides of the joint 3. 7

One terminal of the secondary winding I31 of the impedance transformer is connected in series with a condenser AC2 with the tube grid 32, while the other terminal of this winding is connected to the center tap of the secondary winding '38 of the transformer ATI, and thereby to the secondary winding 42 of the transformer ATI and also to the cathode 34 of ,the tube.

The grid of the tube is connected to the other terminal of the transformer secondary winding 42 through a resistor ARI.

Inthe operation of this system current supplied by thesecondary winding 42 of the trans former ATI flows in the grid circuit which is traced from one terminal of the winding 42 through the winding I31 of the impedance transformer I35, condenser AC2, resistors ARI and AR2, and condenser AC3 to the other terminal of secondary winding 42.

At this time, assuming that the track stretch is unoccupied, thecircuit of the primary winding I36 of the impedance transformer I35 is open, and the impedance of this winding is relatively high, while the impedance of the secondary winding is correspondingly high.

As a result of the high impedance of the winding I31, there is a relatively large drop in potential between thetube grid"32 andthe cathode 34. The various parts of the equipment are chosen so that the grid potential at this time is such that the tube is rendered conducting during the half cycle intervals in which the tube anode is positive with respect to the tube anode.-

The relay AREI, therefore, is energized and it will continue to be energized as long as the track stretch at station A is unoccupied.

When the track section is occupied by a train, the wheels and axles of the vehicles of the train provide connections between the track rails and thereby establish a circuit between the portions of the rail 2 at opposite sides of the joint 3 and thus complete the circuit through the winding I36 of the impedance transformer I35. This circuit may be traced from one terminal of the winding I36 to the track rail 2 at one side of the joint 3, thence to the track rail I by the path through the wheels and axle of a vehicle,

along the track rail I and back to the track rail 2 through the wheels and axle of a vehicle at a point on the other side of the joint 3, and then to the other terminal of the winding I36.

As a result of the completion of this circuit through the winding I36, the impedance of the winding is greatly reduced, while there is a corresponding reduction in the impedance of the winding I31. On this reduction in the impedance of the winding I31 there is a reduction in the difference in potential between the tube grid 32 and its cathode 34. The various parts of the system are chosen so that this reduction in the grid potential is such that the tube is no longer conducting. The relay AREI, therefore, is deenergized and remains deenergized as long as the train or a vehicle bridges the joint 3 at station A, while the relay will again be energized when the train no longer bridges the joint 3.

The train detecting means shown in this figure of the drawings is adapted to be employed in connection with timing means of the type shown in Figs. 1A and 13, if desired, to control the operation of a crossing signal in accordance with the speed of the train approaching the intersection protected by the signal.

It will be seen that this invention provides means to detect the passage of a train through a track stretch and to also measure the speed of the train to thereby determine the point in the track stretch to which the train must advance before operation of the highway crossing signal is initiated.

In addition it will be seen that this invention provides several forms of train detecting means and that either of these may be employed in connection with the timing means.

While the train detecting means and the timing means have been described in connection with a control system for a highway crossing signal, it should be understood that they are not limited to use in this connection and that it is contemplated that they may be employed wherever the results which they provide are desired.

Although I have herein shown and described a complete system for controlling a highway crossing signal, together with several modified forms of train detecting means, it should be understood that various changes and modifications may be made therein within the scope of the appended claims without departing from the spirit and scope of my invention.

Having thus described my invention, what I section controlling said circuit, a first and a sec- 0nd timing means also controlling said circuit, the device associated with the station farthest removed from the intersection and the device associated with the station next farthest removed from the intersection jointly controlling the first timing means, the device associated with said station next farthest removed from the intersection and the device associated with the adjacent station in advance thereof jointly controlling said second timing means.

2. In combination, a stretch of railway track having an intersection with a highway, a crossing signal for protecting said intersection, a plurality of train detecting stations located at points in said track stretch progressively farther in the rear of said intersection, each of said stations having a train detecting device responsive to the presence of a train in said track stretch at said station, each of said devices except the device associated with the station farthest removed from the intersection controlling a circuit for controlling the crossing signal, timing means comprising a condenser, an element connected in parallel with said condenser and being adapted to become conducting when and only when current of a predetermined potential is supplied thereto, and a relay having its winding connected in series with said element whereby said relay winding is energized when said element is conducting, said relay controlling the circuit for controlling the crossing signal, means controlled by the device associated with the station farthest removed from the intersection for initiating the supply of current to the circuit of said condenser and said element, and means controlled by the device associated with the station next farthest removed from the intersection for interrupting the supply of current to the circuit of said condenser and said element.

3. In combination, a stretch of railway track having an intersection with a highway. a crossing signal for protecting said intersection, a plurality oftrain detecting stations located at points in said track stretch, progressively farther in the rear of said intersection, each of said stations having a train detecting device responsive to the presence of a train in said track stretch at said station, each of said devices except the device associated with the station farthest removed from the intersection controlling a circuit for controlling the crossing signal, timing means comprising a condenser, an element connected in parallel with said condenser and being adapted to A become conducting when and only when current of a predetermined potential is supplied 'thereto,-

and a relay having its winding connected in series with said element whereby said relay winding is energized when said element is conducting, said relay controlling the circuit for controlling the crossing signal, means controlled by the train detecting device associated with the station farthest removed from the intersection for initiating the supply of current to the circuit of said con-" denser and said element, means controlled by the device associated with the station next farthest removed from the intersection for interrupting the supply of current to the circuit of said condenser and said element, and means controlled Jointly by said relay and by the train detecting device associated with the said station next farthest removed from said intersection for supplying current over a circuit shunting said element to energize said relay.

4. In combination, a stretch of railway track having an intersection with a highway, a crossing signal for protecting said intersection, a plurality of train detecting stations located at points in said track stretch progressively farther in the rear of said intersection, each of said stations having a train detecting device responsive to the presence of a train in said track stretch at said associated with the station farthest removed from the intersection controlling a circuit for controlling the crossing signal, timing means comprising a condenser, an element connected in parallel with said condenser and being adapted to become conducting when and only when current of a predetermined potential is supplied thereto, and a relay having its winding connected in series with said element whereby said relay winding is energized when said element is conducting, said relay controlling the circuit for controlling the crossing signal, means controlled by the train detecting device associated with the station farthest removed from the intersection for initiating the supply of current to the circuit of said condenser and said element, means controlled by the device associated with the station next farthest removed from the intersection for interrupting the supply of current to the circuit of said condenser and said element, and means controlled by the said train detecting device associated with the station next farthest removed from the intersection for dissipating a charge established on the condenser.

5. In combination, a stretch of railway track having an intersection with a highway, a crossing signal for protecting said intersection, a plurality of train detecting stations located at points in said track stretch progressively farther in the rear of said intersection, each of said stations having a train detecting device responsive to the presence of a train in said track stretch at said station, each of said devices except the device associated with the station farthest removed from the intersection controlling a circuit for controlling the crossing signal, timing means comprising a condenser, an element connected in parallel with said condenser and being adapted to become rent to the circuit of said condenser and said element, means controlled by the device associated with the station next farthest removed from the intersection for interrupting the supply of current to the circuit of said condenser and said element, and means controlled jointly by the train detecting device associated with the sta-- tion farthest removed from the intersection, the

device associated with the station next farthest removed from the intersection, and the relay of said timing means for supplying current over a circuit including said element in series to energize said relay.

6. In combination, a stretch of railway track having an intersection with a highway, a crossing signal for protecting said intersection, a plurality of train detecting stations located at points in said track stretch progressively farther in the rear of said intersection, each of said stations having a train detecting device responsive to the presence of a train in said track stretch at said station, each of said devices except the device associated with the station farthest removed from the intersection controlling a circuit for controllingthecrossingsignal,timing means comprising a condenser, an element connected in parallel with said condenser and being adapted to become conducting when and only when current 

